# The Oblique Orbit of WASP-107b from K2 Photometry

## TL;DR

This study uses K2 photometry to analyze the oblique orbit of WASP-107b, revealing high stellar obliquity and suggesting a link between star-planet alignment and planetary orbit characteristics.

## Contribution

It provides the first evidence of high obliquity for a low-mass star hosting a warm Jupiter, challenging existing theories on obliquity excitation.

## Key findings

- Stellar rotation period confirmed at 17 days.
- Evidence for high obliquity between 40-140 degrees.
- Connection between stellar obliquity and planet orbital properties.

## Abstract

Observations of nine transits of WASP-107 during the {\it K2} mission reveal three separate occasions when the planet crossed in front of a starspot. The data confirm the stellar rotation period to be 17 days --- approximately three times the planet's orbital period --- and suggest that large spots persist for at least one full rotation. If the star had a low obliquity, at least two additional spot crossings should have been observed. They were not observed, giving evidence for a high obliquity. We use a simple geometric model to show that the obliquity is likely in the range 40-140$^\circ$, i.e., both spin-orbit alignment and anti-alignment can be ruled out. WASP-107 thereby joins the small collection of relatively low-mass stars hosting a giant planet with a high obliquity. Most such stars have been observed to have low obliquities; all the exceptions, including WASP-107, involve planets with relatively wide orbits ("warm Jupiters", with $a_{\rm min}/R_\star \gtrsim 8$). This demonstrates a connection between stellar obliquity and planet properties, in contradiction to some theories for obliquity excitation.